I'm sorry but I'm still stupid about this.
Why not just closed rather than delete it ? AFAIK by closed the thread , everyone will not able to reply anymore.
I'm just afraid if they send the thread into trash can and new member try to created similar topic that have been trash can. ( they search the title first )
I think it's can be like endless loop , happen all the time.
I think deleting a thread will be the most effective rather than closing a thread and move it to archival since as you said newbies here in forum will create the same thing over again and it always happens even there is a thread about it and also, mega spam threads just like in bitcoin and altcoin discussions with 40-100 pages of the same answer will make forum dirty so deleting them will make the forum cleaner and saves a lot of space.